Most chess sites provide a "firehose" for current games. It should be pretty easy to pipe a game's pgn file to stockfish. Also, sites also have a "viewer" page

Most chess sites provide a "firehose" for current games. It should be pretty easy to pipe a game's pgn file to stockfish. Also, sites also have a "viewer" page for most games where they add a chess engine evaluation of the current position. All you really need to do to cheat is to open your game under another account and you can just copy over the move in the top line. If you are interested in super computer evaluation of chess games, [sesse](https://analysis.sesse.net https://analysis.sesse.net) usually has the analysis of the "game of the day". It's run by people at chess24, so they usually analyze Magnus' games.